1. Field of the Invention
The present invention relates to an image display device, a driving circuit and, a driving method to be used in the image display device and more particularly to the image display device in which, when a moving picture is displayed by using a holding-type display panel such as a liquid crystal panel which holds a current frame until display data corresponding to a succeeding frame is supplied, a black insertion driving operation to insert one black frame between two continuous frames in a repeated manner is performed, and to the driving circuit and driving method to be used in the above image display device.
The present application claims priority of Japanese Patent Application No. 2005-347156 filed on Nov. 30, 2005, which is hereby incorporated by reference.
2. Description of the Related Art
A liquid crystal display device is generally driven in a holding-type manner in which a current frame is held until display data corresponding to a succeeding frame is supplied. As a result, in principle, there is no flicker in the display which can provide easiness on the eyes. In this case, a device used to mainly display a still image, such as a personal computer or a like presents no problem, however, in the case of a display device to display a moving picture such as a liquid crystal television set, a subsequent image is displayed with a current image being still left in the consciousness of a user and, as a result, the current image is perceived by a user as an afterimage. On the other hand, a CRT (Cathode Ray Tube) display device is generally called an “Impulse-type” display device in which, immediately after light is intensively emitted for a moment, light disappears, and nothing is displayed until subsequent displaying starts. This operation is repeated, for example, at the frequency of 60 times per second. Thus, subsequent displaying does not start until an image previously displayed disappears and, therefore, in the case of displaying a moving picture, the persistence of vision is less perceived by a user. Due to this, in a liquid crystal display device, in a liquid crystal television set in particular, in order to achieve the “impulse-type” displaying, an effort to reduce the persistence of vision is being made by inserting one black frame between two continuous frames in a repeated manner.
The conventional liquid crystal display device of this type includes, as shown in FIG. 11, a black insertion driving control section 1, a source driver 2, a gate driver 3, and a liquid crystal panel 4. The liquid crystal panel 4 has data electrodes (not shown), scanning electrodes (not shown), and liquid crystal cells (not shown). In the liquid crystal panel 4, scanning signals “OUT” are sequentially supplied to the scanning electrodes and corresponding pixel data “D” are supplied to the data electrodes and, as a result, corresponding pixel data “D” are fed to corresponding liquid crystal cells in which modulation is then performed on light emitted from a backlight (not shown) to form an image to be displayed. The source driver 2 applies, based on a control signal “a” fed from the black insertion driving control section 1, a voltage for pixel data “D” corresponding to a video input signal “VD” to each of the data electrodes in the liquid crystal panel 4. The gate driver 3 applies a scanning signal “OUT”, based on a control signal “b” fed from the black insertion driving control section 1, line-sequentially, to each of the scanning electrodes in the liquid crystal panel 4. The black insertion driving control section 1 sends out, based on the video input signal “VD”, a control signal “a” to the source driver 2 and a control signal “b” to the gate driver 3 so as to perform the black insertion driving operation so that one black frame having a gray level of, for example, “0” is inserted between two continuous frames in the liquid crystal panel 4 uniformly and in a repeated manner.
Conventional technologies of this type, in addition to the above conventional liquid crystal display device, are disclosed, for example, in following references.
In the conventional liquid crystal display device disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2003-186456, abstract, FIG. 1), data screen and a black screen appear for one frame period alternately at over twice faster than normal speed. Particularly, in image display for adjacent frames, a black display region and a data display region change their places alternately. As a result, when moving pictures are being displayed, portions in which a response speed is high and portions in which a response speed is low exist in a mixed manner, thus suppressing an image distortion and a feeling of the persistence of vision.
In frame interpolation technology disclosed in Non-Patent Reference 1 (Gou Sato, “Frame interpolation technology for displaying moving pictures having more natural images”, Homepage “R & D Forefront” Toshiba Review, Vol. 59 No. 12, 2004), motion estimation is performed base on two original image frames to form interpolated frames which are inserted for one frame period. As a result, each frame maintains brightness with an afterimage being reduced.
However, the above conventional liquid crystal display devices have the problems described below.
That is, in the conventional liquid crystal display device shown in FIG. 11, since black frames are inserted uniformly irrespective of shades of gray set for every frame, though an effect of reducing afterimages at time of displaying moving pictures can be obtained, gray-level displaying effects decrease and contrast is lowered, as a result, making it difficult to achieve sufficient improvement in displaying moving pictures. In order to obtain compatibility between the effect of improving display of moving pictures and the effect of enhancing gray-level displaying and contrast, a great increase in luminance of backlight is required, which causes an increase in manufacturing costs for the backlight and in power consumption.
Also, in the liquid crystal display device disclosed in the Patent Reference 1, data screen and a black screen appear for one frame period alternately at over twice faster than normal speed to suppress the image distortion and feeling of the persistence of vision and, therefore, the object of the invention disclosed in the Patent Reference 1 is very similar to that of the present invention, however, both are different from each other in terms of the configurations of the liquid crystal display device.
In the frame interpolation technology disclosed in the Non-Patent Reference 1, the object of the invention disclosed in the Non-Patent Reference is very similar to that of the present invention, however, additional devices for motion estimation are required in the conventional technology, a problem arises that hardware configurations of the liquid crystal display device become complicated.